As the demand for petroleum (oil) increases, and the supply of available petroleum declines, the world seeks ways to more efficiently and completely employ that supply in production of useable power—such as electricity generation. While great strides have been made in developing various alternate energy technologies, including nuclear, hydroelectric, wind and solar, fossil fuels still drive the majority of the world's electrical generators. Typically, such generators run on steam, which is heated by burning coal, gas or oil. Some generators employ direct gas turbine technology, but these are largely used in backup, and peak capacity roles. In the US, coal and natural gas are the primary fossil fuels employed in large-scale power generation. However, oil is an important source as well, particularly in smaller scale plants. Oil is also the key ingredient in the manufacture of many plastics and polycarbonates.
Supplies of high-grade crude oil are becoming scarcer, and the increasing price of oil has motivated drillers to pursue sources that are more costly to extract and contain higher degrees of waste products. One example is the extraction of oil from oil sands or shale, which entails significant energy in driving the oil from the sand/rock layers. In almost all combustion applications the oil must be essentially solid-free to be used as a fuel. This is because the combustion of oil typically entails injecting it through a nozzle into a combustion chamber to form an atomized mist that mixes with blown-in makeup air. Any suspended solids in the injected oil would clog the nozzle, and cake-up within the combustion chamber and exhaust system. Thus, simply combusting the solids and oil together is not practical.
More generally a typical oil well in many regions produces a mixture of oil, salt brine water and fines of dirt, dust and sand, referred to in the industry as SWD. This mixture is often referred to as “oil sludge”. For example, the product of a typical developed producing well can consist of approximately a 50/50 mix of oil and water, with approximately 20%-30% oil-covered (or oil-impregnated) sludge. The water is a substantially salty brine, forming an emulsion of oil, water and salt. This sludge is withdrawn from the well with the oil product as production sludge throughout the life of the well. During production, the withdrawn oil is initially pumped from the well into a battery of storage tanks. Within these tanks, the sludge is allowed to settle to the bottom, and the oil product is periodically withdrawn and transported by a tank truck to a refinery. The storage tanks are periodically cleaned, with the bottom layer of settled sludge being removed by, for example, a vacuum truck. The sludge is then transported to a sludge pit. This is a typical technique for disposing of this byproduct, whereby the sludge is concentrated in sludge pits. The technique allows the water to settle as the emulsion breaks over one to two days. Some or all of the water is then allowed to evaporate, or it is actively separated-out by skimmers and pumps. Any separated water is then injected into a deep well. The sludge itself is trucked to a bury pit, mixed with enough fresh dirt to retain all the liquid oil residues, buried and the pit is eventually capped off, or simply left exposed. One reason no further processing is attempted is that the oil suspended in the sludge is challenging and costly to extract from the mixture.
Clearly, this is an unacceptable waste and abandonment of an energy-rich petroleum product, which has an energy density approaching 14,500 Btu per pound. By contrast the heat content of coal ranges from approximately 7,600 to 15,000 BTU per pound, evidencing the significant, foregone energy potential inherent in oil sludge. Moreover, the use of sludge pits presents a long-term environmental hazard that has the potential to endanger ground water supplies, animal life and human health. It is, thus desirable to provide a system and method that allows oil with suspended solids (clay, sand, shale, etc.) to be fully exploited for their energy value in, for example, the generation of steam that can drive an electrical generator and/or heating devices. The system and method should desirably handle the oil/solid mixture with minimal pre-processing of the mixture so as to avoid the application of excessive process energy in preparing the mixture for use as a fuel. Moreover, the temperatures at which this mixture is burnt to generate usable heat should be sufficient to ensure complete combustion, which in turn reduces harmful exhaust emissions.